Method for Sizing and Overflow on an Atmospheric Tank
Method for Sizing and Overflow on an Atmospheric Tank
(OP)
Is there an accepted/recommended method for sizing an overflow for an atmospheric tank where an independent vent line is also incorporated
The tank I am looking at contains hot water and has an independent vent line coming off the top. It also has an overflow set ~ 0.5 m from tan line coming out of the vertical vessel wall
I have seen various articles regarding self venting flows and Froude Nos. These appear to be applicable only when the vent is also the overflow?
If I size based on a self venting flow, the overflow line size seems excessive to me (nearly .08 m at a flow of 0.33m³/sec)
Is this correct, or can I reduce the size and accept that the flow doesn't have to be self venting as there is a separate vent line.
Is it accepatble to assume the overflow line is flooded to a set height and then work out the flow based on static head as the driving force
The tank I am looking at contains hot water and has an independent vent line coming off the top. It also has an overflow set ~ 0.5 m from tan line coming out of the vertical vessel wall
I have seen various articles regarding self venting flows and Froude Nos. These appear to be applicable only when the vent is also the overflow?
If I size based on a self venting flow, the overflow line size seems excessive to me (nearly .08 m at a flow of 0.33m³/sec)
Is this correct, or can I reduce the size and accept that the flow doesn't have to be self venting as there is a separate vent line.
Is it accepatble to assume the overflow line is flooded to a set height and then work out the flow based on static head as the driving force





RE: Method for Sizing and Overflow on an Atmospheric Tank
Undersizing the overflow on an atmospheric tank can and often has resulted in a rounded bottom on a formerly flat-bottomed tank, should there ever be an upset.
RE: Method for Sizing and Overflow on an Atmospheric Tank
The overflow size should read 0.8 m rather than 0.08 m as I stated earlier
RE: Method for Sizing and Overflow on an Atmospheric Tank
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RE: Method for Sizing and Overflow on an Atmospheric Tank
you may want to have a look at "Applied Chemical Process Design" by F. Aerstin & G. Street. There you will find a diagram for sizing discharge lines from gravity decanters. With the given flowrate (5230 gpm) a 30 inch line seems to be sufficient.
Kind Regards,
hahor
RE: Method for Sizing and Overflow on an Atmospheric Tank
Generally speaking, size an overflow for 2.5 - 3.5 ft/second velocity.
Base your calculation on the maximum filling rate.
A pipe of 26 or 28 inch NPS would be my choice..
-MJC
RE: Method for Sizing and Overflow on an Atmospheric Tank
RE: Method for Sizing and Overflow on an Atmospheric Tank
Where:
Q= Flow in
H= Vertical distance from overflow centre up to upper edge tank
2) Check with: Fr>0.3 (self venting) if a PIPE is connected to the nozzle. However, it is not a VITAL criteria, not satisfying Fr>0.3 just causes some vibration during overflow. The first item is vital.
Hope this help